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Questions Answered: 93

Final Score 68%

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Physiology

Respiratory

Question 60 of 93

All of the following cause bronchoconstriction, EXCEPT for:

Answer:

Factors causing bronchoconstriction:
  • Via muscarinic receptors
    • Parasympathetic stimulation
    • Stimulation of irritant receptors
    • Inflammatory mediators e.g. histamine, prostaglandins, leukotrienes
  • Beta-blockers

Airway Resistance

Airflow is driven by and is directly proportional to, the mouth-alveolar pressure gradient generated by the respiratory muscles.

Flow through airways is described by Darcy's law: Flow = (P1 - P2)/R where P1 is the alveolar pressure, P2 is the mouth pressure and R is the resistance to airflow.

Airway resistance is primarily determined by the airway radius according to Poiseuille's law, and whether the flow is laminar or turbulent. The major site of airway resistance is the medium-sized bronchi. The smallest airways would seem to offer the highest resistance, but they do not because of their branching parallel arrangement.

Factors Affecting Airway Resistance

Factors causing bronchoconstriction:

  • Via muscarinic receptors
    • Parasympathetic stimulation
    • Stimulation of irritant receptors
    • Inflammatory mediators e.g. histamine, prostaglandins, leukotrienes
  • Beta-blockers

Factors causing bronchodilation:

  • Via beta2-adrenoceptors
    • Sympathetic stimulation
    • Adrenaline (epinephrine)
    • Beta2-adrenergic agonists e.g. salbutamol
  • Anticholinergic and muscarinic antagonists e.g. ipratropium

Pollutants, and substances released from mast cells and eosinophils can increase airway resistance via bronchoconstriction, mucosal oedema, mucus hypersecretion, mucus plugging and epithelial shedding - all of which are important in asthma.

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  • Biochemistry
  • Blood Gases
  • Haematology
Biochemistry Normal Value
Sodium 135 – 145 mmol/l
Potassium 3.0 – 4.5 mmol/l
Urea 2.5 – 7.5 mmol/l
Glucose 3.5 – 5.0 mmol/l
Creatinine 35 – 135 μmol/l
Alanine Aminotransferase (ALT) 5 – 35 U/l
Gamma-glutamyl Transferase (GGT) < 65 U/l
Alkaline Phosphatase (ALP) 30 – 135 U/l
Aspartate Aminotransferase (AST) < 40 U/l
Total Protein 60 – 80 g/l
Albumin 35 – 50 g/l
Globulin 2.4 – 3.5 g/dl
Amylase < 70 U/l
Total Bilirubin 3 – 17 μmol/l
Calcium 2.1 – 2.5 mmol/l
Chloride 95 – 105 mmol/l
Phosphate 0.8 – 1.4 mmol/l
Haematology Normal Value
Haemoglobin 11.5 – 16.6 g/dl
White Blood Cells 4.0 – 11.0 x 109/l
Platelets 150 – 450 x 109/l
MCV 80 – 96 fl
MCHC 32 – 36 g/dl
Neutrophils 2.0 – 7.5 x 109/l
Lymphocytes 1.5 – 4.0 x 109/l
Monocytes 0.3 – 1.0 x 109/l
Eosinophils 0.1 – 0.5 x 109/l
Basophils < 0.2 x 109/l
Reticulocytes < 2%
Haematocrit 0.35 – 0.49
Red Cell Distribution Width 11 – 15%
Blood Gases Normal Value
pH 7.35 – 7.45
pO2 11 – 14 kPa
pCO2 4.5 – 6.0 kPa
Base Excess -2 – +2 mmol/l
Bicarbonate 24 – 30 mmol/l
Lactate < 2 mmol/l

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